Could primordial black holes be dark matter?

Sep 21, 2011 by Miranda Marquit

(PhysOrg.com) -- We know that about 25% of the matter in the universe is dark matter, but we dont know what it is, Michael Kesden tells PhysOrg.com. There are a number of different theories about what dark matter could be, but we think one alternative might be very small primordial black holes.

When many of us think about black holes, we think of a huge cosmic event, sucking in everything around it. However, there is also the possibility of small black holes. Einsteins theory of relativity allows for black holes, Kesden, a theoretical physicist at New York University, explains, but doesnt stipulate a size. Its very possible that the early universe produced very small black holes. These would gravitate like massive black holes, floating through the universe and clustering.

Kesden worked with Shravan Hanasoge, from Princeton University and the Max Planck Institute for Solar System Research, to work out method of using solar oscillations to determine whether a small, primordial black hole passed through a star. If the data can show that these small black holes formed near the beginning of the universe do exist, they might make good candidates for dark matter. Their work can be seen in Physical Review Letters: Transient Solar Oscillations Driven by Primordial Black Holes.

Our approach is to consider what happens if you have dark matter made of primordial black holes passing through the sun, Kesden says. Its been thought of before, but no one has actually done the calculations that we have.

Kesden explains that the sun creates energy from the nuclear fusion at its center: There is a balance between the outward pressure gradient due to the energy released by fusion and the inward force of gravity. If the sun, or any star, is perturbed it would shake a little.

A small, primordial black hole would be the size of an atom but have the mass of an asteroid, he points out. Its strong gravitational field, as it cut through the sun, would squeeze it, then release, and cause the sun to oscillate before ultimately settling down.

The idea is to measure the oscillation, and determine what would cause it. Shravan Hanasoge wrote a program to help us with a simulation to see what the sun would look like if a primordial black hole passed through. The smallest mass detectable is 10^21 grams, Kesden continues.

Now that Kesden and Hanasoge know what to look for, it is possible to measure the oscillations of different stars. Since these primordial black holes are thought to be moving through the universe, it should be observable in different stars. By inferring the total amount of dark matter in the universe, it should be able to determine how often a primordial black hole would pass through the sun  if its dark matter, Kesden says. Unfortunately, dark matter would only pass through the sun every millions of years. Thats a long time to stare at our sun, waiting for the event.

Instead of waiting millions of years for a primordial black hole to pass through our sun, it is possible to monitor millions of stars; one of these stars would likely encounter a primordial black hole every few years. Kesden points out that current and future space missions could collect the needed data. It is possible to look at the data collected from asteroseismic missions for these events, now that we know what to look for. Someone could even look through data collected in the past to try to spot these oscillations.

At the Large Hadron Collider, some scientists are trying to determine if supersymmetry is dark matter, Kesden says. But if it isnt found at the LHC, people will begin looking for other alternatives, and primordial black holes might be the answer to the outstanding question of what dark matter is.

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I think that the evaporation of small scale black holes depends on the mass of the black hole, thus a "larger" BH with an asteroid like mass would stick around considerably longer. Though I do not know the details.

Michael Kesden, we know it's ~25% of the CONTENT of the universe, when you throw in Dark Energy, that constitutes dark matter, not ~25% of the matter. Fur gad's sake. (Maybe this was misreported by Ms. Marquit?)

Dark matter existence, or requirement for it, is unproven despite this and many other authors contention. Minor additions to Einstein's equations of gravity can eliminate requirement entirely and are FAR more likely IMHO. Google MOG, John Moffat.

LG100 - adding a fifth, as yet undetected, force and a new force particle is not what I would consider a minor addition. Don't get me wrong though, I love MOG. It is surely a better alternative to DM than a bunch of primordial mathematical artifacts (singularities) floating around.

We know that about 25% of the matter in the universe is dark matter...

The problem is that we do not know that. We only know that our models of gravity do not accurately predict the movement of stars and galaxies.

Not quite, Dogbert. We do not "ONLY know that our models of gravity do not accurately predict the movement of stars and galaxies". We know a little more than that. While you'd be correct to say that we know our models of gravity do not accurately predict the movement of stars and galaxies, we also know that there is non-baryonic matter out there causing gravitational lensing effects and have been able to map this to, IMO, a respectable degree of accuracy. Accurately enough that we know that that non-baryonic something makes up the majority of the mass where gravitational lensing occurs. In some cases there is even lensing where there is no more baryonic matter, i.e., around the Bullet Cluster.

"One might expect even a small black hole, upon colliding with a star, would swallow it completely."

The primordial black holes discussed here are thought to be about the size of a proton and would consume a negligible amount of matter passing through a star.

Several studies have looked at the the possibility of detecting PBHs passing through the Earth and found that no catastrophic effects would occur. In fact, a concerted effort would be needed to detect them at all.

DM is a plug. That doesn't mean there isn't DM, but it is a plug until we directly observe it or get a better hold on what it is. dogbert is wrong because there is more to support DM than just star/galaxy movement. Much more.

On to the theory here, primordial black holes(PBH). PBH would mean Hawking radiation is wrong (nod to uba). I'd go further and say PBH relies on a broken limit in GR's equations that presents itself as infinities within black holes. GR was an improvement on Newtonian gravity, but it isn't the end all. Without singularities PBH theory just becomes little balls of densely packed matter, a.k.a. cold dark matter.

Gawad, btw: Moffat has used MOG to explain CMB data, galaxy formation, lensing data (including Bullet and Abell 520), and expansion. He has moved on to some work with quantum gravity and electro-weak theory. It looks like he is trying to find a why for his fifth force. Many of his MOG papers are no longer available on arxiv.

IMO physicists are getting confused in this point. These primordial black holes are nothing else than just common atom nuclei (protons in particular). And these atom nuclei can be indeed present in huge amount inside of dark matter - I presume, they're forming a significant component of so-called the hot dark matter, whereas the cold dark matter is rather formed with small lightweight particles like the slow (anti)neutrinos.

The problem is that we do not know that. We only know that our models of gravity do not accurately predict the movement of stars and galaxies.

Not quite, Dogbert. We do not "ONLY know that our models of gravity do not accurately predict the movement of stars and galaxies". We know a little more than that. While you'd be correct to say that we know our models of gravity do not accurately predict the movement of stars and galaxies, we also know that there is non-baryonic matter out there causing gravitational lensing effects ...

No, we don't know that. We know only that our models fail to predict the observations -- movements of stars, galaxies and lensing. All of those instances are failures of our gravity models. They are proof of nothing more than that our models don't match our observations.

No, we don't know that. We know only that our models fail to predict the observations -- movements of stars, galaxies and lensing. All of those instances are failures of our gravity models. They are proof of nothing more than that our models don't match our observations.

Not exactly.

The 'dark matter model' is really a number of models that rely on massive particles that do not interact strongly with EM radiation. Scientists use the metaphor "Dark Matter" to describe this new matter in these models. And indeed many of these models can fit quite well with observations, without changing gravity.

Of course, on the other hand, many models which change gravity can indeed fit the observations as well, without requiring the Dark Matter metaphor.

We're waiting on better observational experiments to determine which models shake out best.

Remember though, the idea that observations point to failures of gravity is only equally as valid as Dark Matter theories

Remember though, the idea that observations point to failures of gravity is only equally as valid as Dark Matter theories

No. Our models of gravitation fail to match our observations. We only know that. We do not know if our models are incorrect or if there is some other reason (such as dark matter) that causes our models to fail.

There is no theory of dark matter. Dark matter was created to explain why our models failed. It does not explain why our models fail. It does not even explain what dark matter is supposed to be. Dark matter was and remains a kludge.

All that we KNOW is that our models fail to match observations.

We may discover something like dark matter. We may not. We certainly have not discovered it yet.

dark matter is the only known cause (or link) to what is called "gravity", and not the Higgs boson, which is only a theory. To undestand "gravity", we must understand how dark matter "creates" or is linked to it and explains how gravity works.

The simplest explanation for dark matter is that it is a plasma of virtual fermion-antifermion pairs inside the vacuum with w = -1. This gravitates clumping to smaller scales. Dark energy is then virtual bosons with w = -1 that anti gravitates spreading out to the largest distance scales.I doubt that the black holes can explain dark matter. PS w = -1 fermion vacuum loops mimic w = 0 CDM (Cold Dark Matter).Jack Sarfatti

You cannot just go spilling random ideas about, specially if they rely on "virtual fermion-antifermion pairs inside the vacuum " These aren't enough to explain how there is more than 6 times the amount of baryonic matter we observe.

Remember though, the idea that observations point to failures of gravity is only equally as valid as Dark Matter theories

No. Our models of gravitation fail to match our observations. We only know that. We do not know if our models are incorrect or if there is some other reason (such as dark matter) that causes our models to fail.

There is no theory of dark matter. Dark matter was created to explain why our models failed. It does not explain why our models fail. It does not even explain what dark matter is supposed to be. Dark matter was and remains a kludge.

All that we KNOW is that our models fail to match observations.

We may discover something like dark matter. We may not. We certainly have not discovered it yet.

If Hawking is correct, the evaporation time of a small black hole is inversely proportional to the cube of is mass. A black hole of ~4x10^5 kg (400 tons) would last about one second. The universe is thought to be ~4x10^17 seconds, so primordial black holes born at ~3x10^11 kg should be evaporating about now.A primordial black hole of 10^21g = 10^18 kg would be ~3x10^6 more massive and would have lost less than ~9x10^12 as much mass so far. That's less than 30 grams, or less than one ounce.

Its very possible that the early universe produced very small black holes. These would gravitate like massive black holes, floating through the universe and clustering

But surely such conventional gravitational clustering would lead to extreme clmupiness as opposed to diffuse accumulations, which is one of the attributes of DM? Can someone clarify that?

Also, I've noticed lately quite a few articles have the phrase "xxx tells PhysOrg.com". Is this an attempt to make it seem as if PhysOrg is actually sourcing/producing these articles rather than getting them from other sources?

Also, I've noticed lately quite a few articles have the phrase "xxx tells PhysOrg.com". Is this an attempt to make it seem as if PhysOrg is actually sourcing/producing these articles rather than getting them from other sources?

To synthesise Dogbert and Temple:Dogbert:'Our models of gravitation fail to match our observations. We only know that. We do not know if our models are incorrect or if there is some other reason (such as dark matter) that causes our models to fail. ' - this is absolutely true.Temple, models of DM are created in order to fit with observations, but they are a kludge, there is no reason to suspect the existance of DM except the failure of previous models to match or explain observations as alluded to by Dogbert. Its not like the DM and MOG are the only contenders, this is one of those cases where the best answer is 'we dont know what causes observations to contradict predictions based on theory'.

DM is a plug. That doesn't mean there isn't DM, but it is a plug until we directly observe it or get a better hold on what it is. dogbert is wrong because there is more to support DM than just star/galaxy movement. Much more.On to the theory here, primordial black holes(PBH). PBH would mean Hawking radiation is wrong (nod to uba).

I agree with Pyle. Open mind, but not dogmatic. As for myself, I'm having some doubts about the existence of 'mini'-sized black hole theory in general (note that I don't discount the possibility of primordial (early formation), just minimum size assertions.) My reservations are based on the following reasoning:Firstly, what does it take to create BH today? The collapse of of a star that is heavier and denser than a neutron star. A BH must be dense enough to generate a gravitional effect that is stronger than its internal pressure. When it comes to size, there is a direct relationship between mass & density. Therefore there must be..cont

cont...a minimum amount of mass, for the gravitational field to be strong enough to crush the star back in on itself to reach BH status. Even allowing for the greater densities as mentioned in wiki, (but densities of what? wiki doen't actually say)& assuming we are talking about external density, I would think that, as soon as the universe started becoming less dense, something the size of an atom and the mass of an asteroid (assumed size of PBH mentioned in the article) would have lost cohesion a very, very long time ago. Please correct if I am wrong, but the size of a BH, tends be be at least 1 kilometer across. Not nanometers. The other problem, when speaking of comparative masses is that asteroids come in a large variety of sizes & the author was remiss in giving any indication of even large or small. The mathematics might look good on paper, but do they really translate? http://en.wikiped...ack_holeSo the whole thing could be a moot point.What do others think? DH66

DarkHorse - No one knows whether primordial black holes were formed.A black hole's event horizon radius is proportional to its mass. A Stellar mass black hole would indeed be a few km in radius.A very small black hole would have to be very dense even compared to a nucleus, but it would not need cohesion other than gravity.The article did give the example of 10^21 grams. A 10^21 gm black hole (10^18 kg) would be ~1.5x10^-9 meters in radius, or about 3 nanometers in diameter. That's quite a bit bigger than an atom, and a bit bigger than a c60 buckyball (a bit less than 3x the diameter, or about 20x the volume).

Gawad, btw: Moffat has used MOG to explain CMB data, galaxy formation, lensing data...and expansion. He has moved on to some work with quantum gravity and electro-weak theory. It looks like he is trying to find a why for his fifth force.

I haven't followed the development of MOG that closely. After MOND and TeVeS by Bekenstein I started paying less attention to this class of MoG theories and more to ones like DSR (still, no joy). Anyway, I'm not really a huge fan of DM, though lensing data has made me lean more in it's direction. There's clearly something massive and fairly ubiquitous out there, or something behaving that way. It's perfectly reasonable to think that this is the same thing that's wonking up stellar and galaxy motions. AFAIC, DM and MoGs are both still kludgy. Requiring a 5th force for MOG sure doesn't help. What one of the MoGs needs is a good prediction (rather than post-diction). GR needs a successor, so I hope one of the MoGs can point the way.

Is this an attempt to make it seem as if PhysOrg is actually sourcing/producing these articles rather than getting them from other sources?

Ummm, I am pretty sure that Physorg does source some articles. They credit their staff authors anyway. At the bottom of the articles it usually acknowledges the source. If it is Physorg it is usually copyrighted, like this one.

@RealScience. I appreciated and do not dispute your answer. My problem is with the fact that such a small mass (under present day conditions) is completely incapabable of generating the amount of gravity required, to put the event horizon beyond the surface of the object and thus qualify it as a black hole. If I am wrong, what have I omitted to take into account in my earlier argument?Cheers, DH66

Is this an attempt to make it seem as if PhysOrg is actually sourcing/producing these articles rather than getting them from other sources?

Ummm, I am pretty sure that Physorg does source some articles. They credit their staff authors anyway. At the bottom of the articles it usually acknowledges the source. If it is Physorg it is usually copyrighted, like this one.

Yes, they credit article 'authors', but most of these are press releases that anyone can pick up and massage the content. By sourcing, I meant employing scientifically literate journalists that, under their own initiative, go out and get a story from the scientists, such as say New Scientist magazine or Scientific American, etc.

It just struck me that they never used to do this before and now I'm seeing it frequently.

DH - I know of nothing that you have omitted with regard to PRESENT-DAY formation of black holes. Under present day conditions there is NO KNOWN WAY to get such a mass to be compressed to smaller than its event horizon.Even the collisions at CERN can only create a miniature black hole if there are hidden dimensions that cause gravity to be much stronger than Newton's equations predict at very small scales.

However it is theorized that pressures in the big bang might have been sufficient to compress much smaller masses past their event horizons, and that such black holes could survive until the present day. It is to these black holes that the article referred.

As I indicated in my earlier posts, no one knows whether primordial black holes were formed, and Hawking radiation is also unproven. But since the article discussed them, I covered the calculations of the size of such black holes IF they exist, and how long they would last IF they exist and IF Hawking radiation is correct.

The only contributor out of those that precede this is dogbert.All we KNOW is that our theories do not match all of our observations.Which tells us nothing more than that something is missing.Individuals sometimes become a little obsessed with an idea and proclaim it as a proof when it isn't. Such fervor is good in that it stimulates further research, all it needs is that these enthusiasts watch their vocabulary.The danger with such attitudes is that they tend to take science close to religion, where belief does not require proof. That is dangerous territory.Remember, a theory is a theory and remains so until it is proven beyond doubt

It is Gravity that tells us there is more mass in the Universe than optical astronomy can account for. Our models of Galaxy formation through gravitational attraction need revision. Hence we need to form tighter constraintgs on what can be causing the gravitational clustering of galaxies since the visible baryionic matter cannot account for the gravitational effects. On the note of the evaporation of any black hole, it is my understanding that as long as the surronding medium i.e. space is at a higher temperature than the BH itself, The hole will grow not shrink.

It is Gravity that tells us there is more mass in the Universe than optical astronomy can account for. Our models of Galaxy formation through gravitational attraction need revision. Hence we need to form tighter constraints on what can be causing the gravitational clustering of galaxies since the visible baryionic matter cannot account for the gravitational effects. On the note of the evaporation of any black hole, it is my understanding that as long as the surronding medium i.e. space is at a higher temperature than the BH itself, The hole will grow not shrink.

Daleg - Yes, the temperature of the surrounding medium will stop a large black hole from evaporating. I put 'for a small black hole' in relating the evaporation time to the cube of the mass because for a large black hole even the ~2.7K cosmic microwave background is enough to stop its evaporation (at least until the universe cools much further). A black hole of mass ~5x10^22 kg (~2/3 the mass of our moon) would be in equilibrium even with just the microwave background.

In order for this explanation of dark matter (tiny primordial black holes) to be taken seriously, we'll need an explanation as to why these objects have not radiated away their mass. Hawking's calculations would have them vanishing early in the age of the universe, billions of years before today, assuming such objects were created in the Big Bang in the first place.

I haven't heard of any explanation for long-lasting tiny black holes. If there is one, I would truly like to see PhysOrg report on it.

Black holes, galactic rotation, large scale cosmological observations, accelerating expansion, Closed Time-like Loops, etc. are all demonstrations of the limits of our understanding of the universe. We are obviously missing something(s). Scientists speculate that singularities and time travel (BHs and CTLs) exist. They think that dark matter and dark energy explain our observations of rotation, lensing and red shift. But ultimately they're all just hypotheses. Guesses with heaps and heaps of corroborating observations. Well thought out and very well supported. But guesses.

IMHO all of these things demonstrate the limits of General Relativity. MOG might not be the right answer, but I feel it is the right kind of answer. There are too many things wrong with General Relativity for it to be the last set of gravitational equations. We're missing something, and I don't think it is the dark "whatever" that we think it is.

IMO the Universe is just random stuff, which implies, there are less and more complex density fluctuations. We happened to be pretty complex ones (Boltzmann brains), which allows us to observe the rest of Universe in transverse wave at considerable distance. This randomness appears to be of material nature just because we are of material nature too. If it would appear differently, we couldn't observe it.

Whole the appearance of Universe correspond such view. For example, from sufficiently distant perspective our Universe appears like infinite lattice of quite regularly spaced galaxies with large black holes and dark matter areas around them. At the sufficient distance the space and matter blurs together.

The same stuff we would see in 2D at the water surface, if we would observe it at sufficient distance with its own waves, where surface and underwater ripples merge together. It's just geometry of randomness, so to say.

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